Accidental needle sticks from used hypodermic needles can transmit disease. Accordingly, various types of needle shields have been designed to reduce the possibility of accidental sticks.
A needle shield that is hinged near the base of the needle has the advantage of allowing one handed needle reshielding. A number of prior art needle shield assemblies including such needle shields have been developed.
Various means have been provided for locking a hinged needle shield in the closed (needle protecting) position. Deflectable members have been provided in the needle shield for engaging the needle upon shielding and preventing subsequent unshielding of the needle. Such members trap the needle within the needle shield. U.S. Pat. No. 4,664,259 discloses a needle shield including a deflectable member. Locking has also been accomplished by locking engagement of the needle shield with the needle support structure. U.S. Pat. No. 5,746,726 discloses a shielded needle assembly of this type.
Needles are available in a number of gauges and lengths so that they can be used for different purposes. Where a needle shield having a deflectable locking member is used to entrap a needle, it is important that the needle displace the locking member or members as it enters the needle shield cavity. It is also important that, since the needle is entrapped by the deflectable locking member or members, it cannot easily be displaced from the cavity. A relatively large diameter needle can more easily displace a deflectable locking member than a small diameter needle, both entering the needle shield cavity and exiting the cavity. As a needle shield should preferably be usable to protect needles of various sizes, the deflectable locking member or members should be designed such that it is sufficiently flexible to allow even a relatively small diameter needle to deflect it as it enters the needle shield cavity, but provides sufficient resistance to prevent the needle from being re-exposed through the opening of the cavity.
U.S. Pat. No. 5,486,163 discloses a sheath that is described as requiring very little force to open a pair of inwardly biased doors as the needle enters the cavity and a much greater force to open them outwardly to expose the needle. Other needle sheaths have deflectable members in the form of hooks, as shown in U.S. Pat. Nos. 4,664,259, 4,944,731, 5,139,489, 5,681,295 and 5,876,381. Still other sheaths include deflectable members integral with a sidewall thereof and extending away from the cavity opening. U.S. Pat. No. 5,490,841 discloses such a sheath wherein the needle is caused to travel towards the resilient hinge of a deflectable member if one attempts to re-expose it. The free end of the deflectable member engages the opposing sidewall of the sheath to prevent it from opening and thereby allowing release of the needle.